Voltage regulators are circuits that are used to provide a regulated voltage. The regulated voltage can be provided for use by other circuitry. For example, voltage regulators are included in integrated circuits, such as volatile and non-volatile semiconductor memory, to provide regulated internal voltages to circuitry used during operation. The voltage (and/or current) demands made by the circuitry may place varying demand on the regulated voltage, which can cause the magnitude of the regulated voltage to vary as well. Additionally, the voltage of the power supply to which the voltage regulator is coupled may vary due to noise, or may be susceptible to changing temperature conditions of the circuits. The voltage regulator, however, is designed to adjust to the varying need and changes so that the regulated output voltage maintains a relatively stable voltage level.
FIG. 1 illustrates a conventional voltage regulator 100 for providing a regulated output voltage Vccint. The voltage regulator 100 includes a differential amplifier 110 providing an output voltage based on the voltage difference between a reference voltage Vref and a feedback-monitored voltage Vmon. The output of the differential amplifier 110 is coupled to a gate of a p-channel transistor 114 that drives the Vccint voltage in accordance with the output voltage of the differential amplifier 110. Resistances R1 and R2 are coupled in series to the drain of the p-channel transistor 114. The resistance R1, which adjustable by a trim code, is used to set the voltage magnitude of the Vccint voltage. In particular, for the voltage regulator 100 Vccint=(1+R2/R1)×Vref. The trim code adjusts the resistance, and consequently, the magnitude of the Vccint voltage, by discrete amounts. The resistances R1, R2 further provide the Vmon voltage fed back to the differential amplifier 110.
In operation, the magnitude of the Vccint voltage is monitored through a feedback loop providing the Vmon voltage to the differential amplifier 110. In response, the differential amplifier 110 varies the conductivity of the p-channel transistor 114 that drives the Vccint voltage in accordance with the difference between the Vmon voltage and the Vref voltage. When the Vmon voltage is less than the Vref voltage, the differential amplifier 110 provides a voltage to the gate of the p-channel transistor 114 to be more conductive, thereby driving the Vccint voltage to a higher level. Conversely, when Vmon voltage is greater than the Vref voltage, the differential amplifier 110 provides a voltage to the gate of the p-channel transistor 114 to reduce the Vccint voltage. In this manner, the Vccint voltage can be regulated to provide a relatively constant output voltage. The magnitude of the regulated output voltage can be changed by adjusting the resistance of the resistance R1. In particular, increasing the resistance R1 reduces the magnitude of Vccint and decreasing the resistance R1 increases the magnitude of Vccint.
As previously discussed, the adjustable resistance R1 can be adjusted using a trim code to set the regulated output voltage level. A detection current Idet that flows through the resistances R1, R2 varies with changes in the resistance R1. For example, a higher resistance setting results in a decreased Idet current, and conversely, a lower resistance setting results in an increased Idet current. As a result, with a higher resistance setting (and lower Idet), the rate at which a voltage change in Vccint is reflected in the Vmon voltage is slower, in part due to the greater overall impedance resulting from the increased resistance. As a result, the response time of voltage regulator 100 is affected by changes in the resistance R1. The response time is generally a measure of how quickly a change in the Vccint voltage is reflected in the Vmon voltage, and as a result, how quickly the voltage regulator 100 can respond to changes in the Vccint voltage, such as when there is a surge in the voltage (and/or current) demand for the Vccint voltage. It is desirable for the voltage regulator 100 to be able to respond quickly enough to changes in demand such that operation of the system in which the voltage regulator 100 is included is not compromised.